Structures in ChaosFormations of Autonomous Robots in Unsafe Areas

Autonomous robots forming into a line in unknown terrain – Dr. Barbara Kempkes in front of a model

Unexplored ocean floor terrain, foreign planets and dangerous regions in crisis areas – these are situations far from any familiar human environment. In the future, people will have to perform challenging tasks in these areas, tasks that cannot be completed with today's technological possibilities, or only at a great risk. We often use robots today for similar problems in areas that are familiar to us. But what if no one can be close to control the robots? What if there is no infrastructure at all and no external energy sources, but instead, the expectation of unpredictable obstacles?

In such situations, as a matter of principle the deployed robots must act alone and completely autonomously. If they are deployed in a group – which will often be the case in insecure regions – they must constantly coordinate their behavior with each other. But before the robots can handle additional tasks, their movement behavior and communication with each other must be guaranteed – even when the terrain is unknown and potentially dangerous. To act as a group, it makes sense for the robots they form up beforehand.

To meet the harsh conditions in insecure regions, the robots have to follow adequate strategies. The prerequisite is that they can move and thus reach their goal as quickly as possible. Their paths must be similar in length so that all robots consume the same amount of energy and so that no individual robot gets stuck along the way. If the latter happened, the formation would break up.

Dr. Barbara Kempkes, a recent Ph.D. and research assistant in the Algorithms and Complexity research group led by Prof. Dr. Friedhelm Meyer auf der Heide, is researching robot formation issues. In her fundamental research, she is creating theories for exemplary robot deployment. The aim of her research was that the robots utilize local knowledge to arrive at a globally good solution: By using algorithms she guaranteed that a group of robots without central control can act autonomously when distributed throughout the terrain and is capable of forming up.

Two different formation variants are possible, each linked to different conditions: In the Gathering Problem variant, the robots must meet together at a particular location. To achieve this, each robot must know all the other robots within its communication radius. In the Robot Chain Formation variant, several robots must position themselves linearly between two fixed points. Despite the little amount of information they receive from only their two neighbors, the robots are still capable of forming a chain.

Both of these formation variants carry a general challenge: Each robot knows only the fixed radius around itself. It can only receive signals from other robots within this limited radius, and thus it can communicate with just these robots. The essential prerequisite for formation is that the robots form up at the start. With limited information from its environment, the robot must then decide what can be done locally, how to act, and how to form up with the other robots – with high efficiency and simultaneous low energy consumption. Dr. Kempkes has designed the corresponding algorithms for this. Using discrete and also continuous run-time analysis, she was able to clarify how long the robots need for a particular formation. She thus mathematically proved the effectiveness of the two robot formations.

The Robot Chain Formation was already implemented and tested in a bachelor’s thesis on the BeBots, small miniature robots.